This invention relates generally to a governor for an internal combustion engine and more particularly to a turbocharger boost feedback control unit for use with such a governor to control the speed droop characteristics of the engine as load is applied to and removed from the engine.
Internal combustion engines are often equipped with maximum speed governors to insure that the engine does not destroy itself due to runaway if the fuel supply to the engine is not reduced on sudden removal of a driven load. Conventional governors are generally of the mechanical variety including flyweights which are rotated to generate a centrifugal force. The centrifugal force is applied axially to a fuel control shaft, the axial motion of which is opposed by a governor spring. The interaction of the centrifugal force generated by the flyweights and the spring force regulates fuel flow to the engine. Such mechanical governors are used because they are inexpensive and reliable due to their mechanical simplicity.
To insure the stability of an engine controlled by a mechanical governor, the engine speed is allowed to drop slightly as the load on the engine is increased. This speed characteristic is referred to as speed droop and is defined as the percentage change in engine speed from no load to full load as a fraction of the full load speed. A speed droop of at least ten percent (10%) is normally allowed to insure stability of an engine governor system.
Oftentimes, however, a limited speed droop is required in the operation of an engine governor system. For example, an engine which is driving an electrical generator must be maintained at a defined frequency (typically 50 or 60 hertz) within relatively narrow tolerances. Where such engine speed control is required, special governors are normally used which result in an increased cost for the engine governor system. Hydraulicservo governors, with independent drives and elaborate compensating circuits, can be used to maintain speed droop from isochronous to seven percent (7%). Powerful electromagnetic actuators driven by electronic control units are also used to maintain engine speeds by modulating a fuel pump throttle control. Yet another arrangement controls the fuel between the pump and the fuel injecting system under the control of a single stage electro-hydraulic valve. All of these special governors are add-on devices which are capable of precisely controlling the speed of an associated engine. However, all are considerably more expensive than the conventionally used mechanical governors.